The present invention relates to an optical module and a method for producing the optical module, and particularly relates to an optical module of a micro-optics type constituted by a lens, a diffraction grating, a filter, and so on, and a method for producing the optical module.
A micro-optics type optical module is disclosed, for example, in Japanese Patent Laid-Open No. 73020/1997. Micro optical elements such as a lens, a plane mirror, a concave mirror, a filter, a diffraction grating and a prism are individually aligned and fixed to the bottom surface of a box-shaped package having one surface opened. Alternatively, the micro optical elements are aligned and fixed to a plane base.
FIGS. 6A and 6B show an example of an optical multiplexing/demultiplexing device which has a diffraction grating provided in Littrow mounting and which is mounted in a box-shaped package having one surface opened. FIGS. 7A and 7B show another example of the optical multiplexing/demultiplexing device which is mounted on a plane base. These examples are illustrated by the present inventors for comparison purpose with the present invention.
In FIGS. 6A and 6B, an input/output optical fiber array 1, a diffraction grating 3, a polarization compensating filter 5 and a collimator lens 2 are provided in a box-shaped package 18 having a top surface opened. The polarization compensating filter 5 is provided to compensate for the polarization dependency of the diffraction efficiency of the diffraction grating 3. The collimator lens 2 is provided to convert divergent light from an input optical fiber 11 into parallel light and converge diffracted parallel light from the diffraction grating 3 on respective optical fibers 12a of an output optical fiber array 12. Here, the diffraction grating 3, the polarization compensating filter 5 and the collimator lens 2 are aligned and fixed to the box-shaped package 18 through a diffraction grating fixing stage 31, a polarization compensating filter stage 51 and a collimator lens fixing platform 21 respectively, which are disposed on the bottom surface of the box-shaped package 18. The input/output optical fiber array 1 is provided with the input optical fiber 11 and the output optical fiber array 12. The output optical fiber array 12 has a plurality of optical fibers 12a. The box-shaped package 18 has such high rigidity that the shape of the package 18 can be retained against external force. Thus, it is possible to form an optical module which has a stable optical axis and which makes a stable operation against mechanical vibration and stress.
On the other hand, in FIGS. 7A and 7B, an input/output optical fiber array 1, a diffraction grating 3, a polarization compensating filter 5 and a collimator lens 2 are provided on a plane base 17 in the same manner as in FIGS. 6A and 6B. Here, the diffraction grating 3, the polarization compensating filter 5 and the collimator lens 2 are aligned and fixed to the plane base 17 through a diffraction grating fixing stage 31, a polarization compensating filter stage 51 and a collimator lens fixing platform 21, respectively. In this case, the plane base 17 is different from the box-shaped package 18 having one surface opened in FIGS. 6A and 6B in that the plane base 17 has open space. Accordingly, even in the case where small-sized optical components are used, units for finely adjusting the respective optical components, such as a micro-motion stage, can be disposed around the optical module easily. Thus, even in the case where the number of parts is large and even in the case where the optical components are small in size, the optical components can be aligned and fixed.
The related-art optical modules, however, have problems as follows.
That is, when the box-shaped package 18 having one surface opened as shown in FIGS. 6A and 6B is used, the optical components are fixed to the bottom surface of the box-shaped package 18 so that there is a space between each of the optical components and each of the opposite side surfaces of the box-shaped package. Thus, the package becomes large in size compared with the optical components. In addition, though an optical system stable against disturbance such as mechanical vibration or heat shock can be produced in the box-shaped package 18 having one surface opened, each of the optical components cannot be finely adjusted through surface sides but the open surface side. Hence, to align a large number of small-sized optical components densely and accurately, finely adjusting mechanisms such as micro-motion stages interfere with one another mechanically. Thus, it is difficult to finely adjust the plurality of optical components simultaneously, and hence it is difficult to assemble them. In addition, it takes much time to set up the components.
On the other hand, when the plane base 17 shown in FIGS. 7A and 7B is used, the optical components are fixed to the plane base 17 so that there is a distance between each of the optical components and each of the end surfaces of the plane base 17. Thus, the package becomes large in size compared with the optical components. In the case of the plane base 17 there is indeed a space around the optical system so that mechanisms which can finely adjust a plurality of optical components simultaneously can be disposed around the optical module, unlike the case shown in FIGS. 6A and 6B. The plane base 17, however, has a structure in which an optical path as a whole is retained by the surface of the plane base 17, so that the total rigidity of the optical module is lowered. In addition, since the optical components are one-sidedly supported by only the bottom surface of the plane base 17, vibration sympathetic with external vibration is amplified so that the optical axis is apt to fluctuate in response to mechanical vibration and external force. Particularly, when the optical path is made long because of increase in the number of parts, optical stability is apt to be lowered. In addition, to solve this problem, it is necessary to make the plane base 17 very thick. Thus, it is difficult to miniaturize the optical module.
The invention is developed in consideration of such problems in the related art. It is an object of the invention to provide a small-sized optical module in which a large number of small-sized optical components is adjusted and aligned accurately while the optical module makes a stable operation against harsh external force or mechanical vibration and thermal disturbance for use in optical communication.
In case of the optical module shown in FIGS. 6A and 6B, the box-shaped package 18 is so high in rigidity that the box-shaped package 18 cannot be deformed or broken easily even in the case where mechanical impact particularly in a drop test is applied on the box-shaped package 18. The impact is, however, transmitted directly to the respective optical components mounted and fixed inside the box-shaped package 18 by the adhesive agent, so that the optical components may be dropped out due to the separation of the adhesive agent. In addition, when the box-shaped package 18 is made of low expansion glass such as pyrex glass which is a material having a small linear expansion coefficient, thermal stability is excellent but the box-shaped package itself is broken in a drop test carried out on the related-art optical module, so that the related-art optical module loses its function.
On the other hand, it is easy to carry out a method of covering the box-shaped package 18 wholly with a resin casing 201 as shown in FIGS. 8A and 8B. It is, however, necessary to make the resin 1 mm or more thick. As a result, the optical module becomes so thick that it is difficult to mount the optical module on one of electric printed boards arrayed on a stand at narrow intervals of 12.7 mm (a half inch).
Further, when only the optical system of the optical module is to be exchanged to a new one so as to afford a higher function to the optical module, or when a portion of the optical system is to be exchanged to a new one because of a failure in the optical module, it is impossible to exchange only the mounting portion of the optical system to a new one. Hence, the package portion which need not be exchanged to a new one originally cannot help being exchanged to a new one when the mounting portion of the optical system is exchanged to a new one.
The invention is developed in consideration of such problems in the related art. It is an object of the invention to provide a micro-optics type optical module which is constituted by a lens, a diffraction grating, a filter, and so on, chiefly for use in optical communication and which has properties stable against mechanical impact and is thin enough to be mounted on an electric printed board. It is another object of the invention to provide an optical module in which only a required portion can be exchanged to a new one for the improvement of the function or at the time of a failure.